We report findings from an extensive study of the users of a Computer-Aided Drafting (CAD) system. Our observations suggest that the CAD system is used inefficiently, because users approach computer_aided drafting from a T-square metaphor reflecting their past experience with traditional drawing media. This prevents them from discovering and using effectively powerful system commands that have no equivalent in manual techniques. These findings suggest that we should rethink the ways in which CAD users are trained and manuals are written, and that we introduce CAD users to a more strategic use of CAD, particularly to a Detail/Aggregate/Manipulate (DAM) strategy that takes advantage of the compositional logic underlying a design.